A known torque fluctuation absorber is provided, for example, on a drivetrain between an engine and a motor generator (or a transmission) in a hybrid vehicle. The known torque fluctuation absorber absorbs (restrains) torque fluctuations generated by torsion (i.e. torsional vibrations) between the engine and the motor generator (transmission). The known torque fluctuation absorber includes, for example, a damper mechanism that absorbs (restrains) the torque fluctuations by means of an elastic force, a hysteresis mechanism that absorbs (restrains) the torque fluctuations by means of a hysteresis torque generated by friction or the like, and a limiter portion that generates slippage when the torque fluctuations are beyond absorbing capabilities of the damper mechanism and the hysteresis mechanism. In the damper mechanism, window portions are formed in rotary members. Coil springs are accommodated in the window portions. A pair of seat members arranged at ends of each of the coil springs in a circumferential direction of the rotary members is contactable with and separable from ends of each of the window portions in the circumferential direction. In a case where the torsion between the rotary members is generated, the coil springs are compressed to thereby absorb the torque fluctuations due to the torsion.
Such known torque fluctuation absorber is disclosed in JP2003-194095A (hereinafter referred to as Reference 1, see FIG. 1). A stopper portion restricting torsion excessively generated between rotary members (the torsion corresponding to torsional vibrations generated between the rotary member is absorbed by the damper mechanism) is arranged at the known fluctuation absorber disclosed in Reference 1 in order to protect coil springs of the damper mechanism from damage. The stopper portion is configured so that protruding portions formed at the rotary members directly make contact with one another in a rotating direction, thereby restraining the torsion excessively generated between the rotary members. In addition, elastic members are arranged within the respective coil springs of the damper mechanism in order that the stopper portion may absorb a shock generated by the direct contact between the protruding portions of the rotary members in the rotating direction. For example, in the case where the torsion is excessively generated between the rotary members, each of the elastic members is sandwiched between a pair of seat member before the protruding portions in the stopper portion make contact with one another. As a result, the shock by the direct contact between the protruding portions is absorbed. In addition, the stopper portion configured as described above enables a reduction of the size of the damper mechanism. In particular, an axial thickness of the damper mechanism may be decreased.
However, the elastic member is arranged within the coil spring; therefore, a space for arranging therein the elastic member is limited. Accordingly, a range where the elastic member may be retracted and compressed is reduced and a diameter of the elastic member is also reduced. As a result, absorbing capability of the elastic member absorbing the shock generated by the direct contact between the protruding portions may be reduced.
A need thus exists for a torque fluctuation absorber, which is not susceptible to the drawback mentioned above.